1. Field of the Invention
This invention relates generally to temperature measurement devices and specifically to adjustable length thermocouple and/or thermowell mounting systems.
2. Description of the Prior Art
Thermocouples are widely used for temperature measurement of machines and processes in the chemical, petroleum, electronics, food, manufacturing and various other industries. Temperature measurement of chemical processes, for example, requires the placement of thermocouples in process units, such as columns, strippers, scrubbers, and reactors. To ensure reliable, efficient operation and process control, process unit temperature is continuously monitored using several thermocouples embedded at various locations within the process unit. Each thermocouple is typically mounted into the wall of the process unit by threading or otherwise securing the thermocouple through a mounting flange or similar measurement port. The thermocouple secured through a mounting flange may be protected on the process unit interior by a thermowell, which is attached to the internal side of the measurement port and acts to shield the thermocouple from harsh process conditions. Alternatively, the thermocouple may be protected by an integrated thermocouple assembly or armor, where the thermocouple wires are encased within an inner protection tube, an inner filler material, and outer sheath or sheaths, all constructed of various chemical compositions.
The accurate measurement of temperature at a specific location on the interior of a process unit requires that the end of the thermocouple be positioned at the specific location. Currently, the majority of process industries either custom make or special order thermocouples or thermowells of varying lengths in order to facilitate temperature measurement at various locations within the interior of a process unit. A thermowell is a hollow tube in which a thermocouple is mounted and serves to protect the thermocouple from the environment in which it is placed to measure temperature. The fixed length thermocouple or thermowell is secured to the measurement port without the ability to adjust the depth of the thermocouple or thermowell within the process unit. Where harsh process conditions are encountered, a thermocouple or thermowell may have a relatively short operational life before failing. The need for comprehensive temperature measurement therefore requires process unit operators to maintain an extensive inventory of replacement thermocouples or thermowells of varying lengths or to be prepared to have them custom made, in order to satisfy the varying thermocouple or thermowell lengths required at specific measurement locations. Thus, thermocouple or thermowell replacement can be both logistically problematic as well as expensive.
Increasing the service life of thermocouples that operate in harsh environments has been the focus of much research and prior invention. However, improving the ease of thermocouple installation has not received as much attention, especially for thermocouples operating in harsh process conditions that require a thermowell for protection. An adjustable depth thermocouple system has been suggested by Mele in U.S. Pat. Nos. 4,826,540 and 4,963,194 for use in machine bodies. The '540 and '194 systems include a hollow thermocouple fitting having external threads for engagement with the internal threads of a thermocouple orifice or well and internal threads adapted for engagement with the spiral surface features of a conventional or armored thermocouple cable. In the Mele adjustable depth thermocouple system, the thermocouple is threaded through the orifice or well until the thermocouple touches the bottom of the thermocouple orifice and proper compression of the resilient material at the surface of the cable is attained. The thermocouple can then be secured in position using a number of suggested locking methods.
The adjustable thermocouple mounting systems described in the prior art have mainly been designed for use in machine bodies or operations with conditions not requiring the use of a protective thermowell. Adjustable thermocouple mounting systems for use in harsh operation environments, such as severe temperature and pressure, require additional considerations not adequately addressed by the current prior art. For example, U.S. patent application 2003/0026742 of Wu et al. describes an adjustable length thermocouple for a fixed length, non-adjustable thermowell. However, the Wu device will result in measurement error when the tip of the thermocouple is retracted from the end of the fixed length thermowell, because any space between the tip of the thermocouple and the end of the thermowell will insulate the thermocouple. In addition, U.S. Pat. No. 5,674,009 issued to Stark describes an adjustable length thermocouple sheath that can be shortened in length by breaking off segments of the sheath at existing stress fracture points created in and along its shaft. However, the Stark device does not permit lengthening of the sheath shaft or provide an adequate pressure seal once the sheath is shortened.
Specifically, an adjustable thermocouple mounting system for use in harsh operating conditions requires a thermowell that is also adjustable and is arranged to maintain a pressure seal with the machine or process unit after installation, that has adequate safeguards to prevent thermocouple back out or blowout under high pressures, and that provides precise thermocouple positioning at installation. Therefore, an adjustable thermowell mounting system is needed that allows a thermocouple-thermowell assembly to be easily adjusted in length to achieve a proper position within a machine or process unit for accurate temperature measurement.
3. Identification of Objects of the Invention
A primary object of the invention is to provide an adjustable thermowell mounting system that allows a thermocouple-thermowell assembly to be quickly adjusted in length to a desired position within a machine or process unit during field installation.
Another object is to provide an adjustable thermowell mounting system that allows a thermocouple-thermowell assembly to be precisely adjusted in length to a desired position within a machine or process unit during field installation.
Another object is to provide an adjustable thermowell mounting system that maintains a pressure seal with a machine or process unit after the thermocouple-thermowell assembly is installed and adjusted in length to a desired position within a machine or process unit.
Another object is to provide an adjustable thermowell mounting system that prevents thermocouple-thermowell assembly blowout or discharge after a thermocouple-thermowell assembly is installed and adjusted by length to a desired position within a machine or process unit.
Other objects, features, and advantages of the invention will be apparent to one skilled in the art from the following specification and drawings.